It would tie into some of Mandarin's back story, basically Immortus had already been traveling across time helping out conquerors, stealing power from them, and sometimes posing as the past conquerors, spreaders of evil. All of the old masters of their parts of the globe until they overextended themselves or made other mistakes Mandarin teaches lessons about in not repeating history

Immortus was not only Rama Tut in this series but he also quickly skipped to other time periods of the past and went through a phase where he was Alexander the Great and fought the Persians. Nothing he did affected the course of history directly but some small things crept in. he couldn't alter much because he was skipping time and running from the Other, his Other he accidentally gave life when he visited the Dawn of time who is joined to him, and hid in every empire of Earth's history... Those considered great and those considered not so great conquerors, and his ancestor Genghis Khan. Hill/Shield and the Atlanteans/Oracle know some of this, despite Fury's best efforts, as well as probably Wakanda with their advanced Science and communication with the other hidden powers of the world. It's the old conquerors that the Mandarin is interested in, but his focus later on would be ushering along the new masters of evil. The old conquerors would be the old masters of evil, who Immortus allied himself with for a while. Immortus didn't realize he indirectly formed the masters of Evil by affecting Mandarin's ancestor and altering some of his beliefs about the rings.. The rings work, mandarin just doesn't know they do until working with the masters several movies down the line...

Immortus also may have secretly ruled over Genghis Khan's period in history and influences the Mandarin that way through his knowledge of the past and all the past rulers Mandarin studies and studying the rings influenced him to become a terrorist and conqueror. The Mandarin also claims descent from some these other rulers, great Chinese Emperors, and says his bloodline has traveled across the globe, making him a mixture of many cultures, though he expresses his connection to Genghis Khan and Chinese Emperors. Mandarin claims he's also got the bloodline of Alexander the great in him and is intended to lead but wants technology to lead. So basically Immortus became an ancestor of this version of the Mandarin, and Mandarin sees himself as a conqueror and Emperor. Like Genghis Khan he gathers a number of new technologies through his conquests, adopts them, and uses them against his opponents.
Basically Immortus would have been forced to repeat history, and had purposely overextended himself in a number of those Empires and committed the exact same mistakes mandarin is talkiing about not making, on purpose to ensure history could progress and to prevent the Other from the dawn of time from working a lot of magic in this realm. He can't stop the Other from entering Asgard and whispering into the Ears of the Vanir who read prophecy like the people who used to think you could read the future through the cracks in bones in Asian cultures. Explaining some of the more modern/ancient elements in some Thor 2 stuff that actually moved there from the past and future a long time ago, but wouldn't be revealed until Immortus's time travel exploits are revealed.
The Other even tried to use others to take over and conquer Asgard, this time for Thanos because he's working the Titan, and trying to affect powerful leaders from a time as far back as Surtur.

so, the waitress from the trailer is Kang now and no longer Wasp, I see

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